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  <div class="section" id="module-telnetlib">
<span id="telnetlib-telnet-client"></span><h1>21.19. <a class="reference internal" href="#module-telnetlib" title="telnetlib: Telnet client class."><code class="xref py py-mod docutils literal"><span class="pre">telnetlib</span></code></a> — Telnet client<a class="headerlink" href="#module-telnetlib" title="Permalink to this headline">¶</a></h1>
<p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.6/Lib/telnetlib.py">Lib/telnetlib.py</a></p>
<hr class="docutils" id="index-0" />
<p>The <a class="reference internal" href="#module-telnetlib" title="telnetlib: Telnet client class."><code class="xref py py-mod docutils literal"><span class="pre">telnetlib</span></code></a> module provides a <a class="reference internal" href="#telnetlib.Telnet" title="telnetlib.Telnet"><code class="xref py py-class docutils literal"><span class="pre">Telnet</span></code></a> class that implements the
Telnet protocol.  See <span class="target" id="index-1"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc854.html"><strong>RFC 854</strong></a> for details about the protocol. In addition, it
provides symbolic constants for the protocol characters (see below), and for the
telnet options. The symbolic names of the telnet options follow the definitions
in <code class="docutils literal"><span class="pre">arpa/telnet.h</span></code>, with the leading <code class="docutils literal"><span class="pre">TELOPT_</span></code> removed. For symbolic names
of options which are traditionally not included in <code class="docutils literal"><span class="pre">arpa/telnet.h</span></code>, see the
module source itself.</p>
<p>The symbolic constants for the telnet commands are: IAC, DONT, DO, WONT, WILL,
SE (Subnegotiation End), NOP (No Operation), DM (Data Mark), BRK (Break), IP
(Interrupt process), AO (Abort output), AYT (Are You There), EC (Erase
Character), EL (Erase Line), GA (Go Ahead), SB (Subnegotiation Begin).</p>
<dl class="class">
<dt id="telnetlib.Telnet">
<em class="property">class </em><code class="descclassname">telnetlib.</code><code class="descname">Telnet</code><span class="sig-paren">(</span><em>host=None</em>, <em>port=0</em><span class="optional">[</span>, <em>timeout</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#telnetlib.Telnet" title="Permalink to this definition">¶</a></dt>
<dd><p><a class="reference internal" href="#telnetlib.Telnet" title="telnetlib.Telnet"><code class="xref py py-class docutils literal"><span class="pre">Telnet</span></code></a> represents a connection to a Telnet server. The instance is
initially not connected by default; the <a class="reference internal" href="functions.html#open" title="open"><code class="xref py py-meth docutils literal"><span class="pre">open()</span></code></a> method must be used to
establish a connection.  Alternatively, the host name and optional port
number can be passed to the constructor too, in which case the connection to
the server will be established before the constructor returns.  The optional
<em>timeout</em> parameter specifies a timeout in seconds for blocking operations
like the connection attempt (if not specified, the global default timeout
setting will be used).</p>
<p>Do not reopen an already connected instance.</p>
<p>This class has many <code class="xref py py-meth docutils literal"><span class="pre">read_*()</span></code> methods.  Note that some of them  raise
<a class="reference internal" href="exceptions.html#EOFError" title="EOFError"><code class="xref py py-exc docutils literal"><span class="pre">EOFError</span></code></a> when the end of the connection is read, because they can return
an empty string for other reasons.  See the individual descriptions below.</p>
<p>A <a class="reference internal" href="#telnetlib.Telnet" title="telnetlib.Telnet"><code class="xref py py-class docutils literal"><span class="pre">Telnet</span></code></a> object is a context manager and can be used in a
<a class="reference internal" href="../reference/compound_stmts.html#with"><code class="xref std std-keyword docutils literal"><span class="pre">with</span></code></a> statement.  When the <a class="reference internal" href="../reference/compound_stmts.html#with"><code class="xref std std-keyword docutils literal"><span class="pre">with</span></code></a> block ends, the
<a class="reference internal" href="#telnetlib.Telnet.close" title="telnetlib.Telnet.close"><code class="xref py py-meth docutils literal"><span class="pre">close()</span></code></a> method is called:</p>
<div class="highlight-python3"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">from</span> <span class="nn">telnetlib</span> <span class="k">import</span> <span class="n">Telnet</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">with</span> <span class="n">Telnet</span><span class="p">(</span><span class="s1">&#39;localhost&#39;</span><span class="p">,</span> <span class="mi">23</span><span class="p">)</span> <span class="k">as</span> <span class="n">tn</span><span class="p">:</span>
<span class="gp">... </span>    <span class="n">tn</span><span class="o">.</span><span class="n">interact</span><span class="p">()</span>
<span class="gp">...</span>
</pre></div>
</div>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.6: </span>Context manager support added</p>
</div>
</dd></dl>

<div class="admonition seealso">
<p class="first admonition-title">See also</p>
<dl class="last docutils">
<dt><span class="target" id="index-2"></span><a class="rfc reference external" href="https://tools.ietf.org/html/rfc854.html"><strong>RFC 854</strong></a> - Telnet Protocol Specification</dt>
<dd>Definition of the Telnet protocol.</dd>
</dl>
</div>
<div class="section" id="telnet-objects">
<span id="id1"></span><h2>21.19.1. Telnet Objects<a class="headerlink" href="#telnet-objects" title="Permalink to this headline">¶</a></h2>
<p><a class="reference internal" href="#telnetlib.Telnet" title="telnetlib.Telnet"><code class="xref py py-class docutils literal"><span class="pre">Telnet</span></code></a> instances have the following methods:</p>
<dl class="method">
<dt id="telnetlib.Telnet.read_until">
<code class="descclassname">Telnet.</code><code class="descname">read_until</code><span class="sig-paren">(</span><em>expected</em>, <em>timeout=None</em><span class="sig-paren">)</span><a class="headerlink" href="#telnetlib.Telnet.read_until" title="Permalink to this definition">¶</a></dt>
<dd><p>Read until a given byte string, <em>expected</em>, is encountered or until <em>timeout</em>
seconds have passed.</p>
<p>When no match is found, return whatever is available instead, possibly empty
bytes.  Raise <a class="reference internal" href="exceptions.html#EOFError" title="EOFError"><code class="xref py py-exc docutils literal"><span class="pre">EOFError</span></code></a> if the connection is closed and no cooked data
is available.</p>
</dd></dl>

<dl class="method">
<dt id="telnetlib.Telnet.read_all">
<code class="descclassname">Telnet.</code><code class="descname">read_all</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#telnetlib.Telnet.read_all" title="Permalink to this definition">¶</a></dt>
<dd><p>Read all data until EOF as bytes; block until connection closed.</p>
</dd></dl>

<dl class="method">
<dt id="telnetlib.Telnet.read_some">
<code class="descclassname">Telnet.</code><code class="descname">read_some</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#telnetlib.Telnet.read_some" title="Permalink to this definition">¶</a></dt>
<dd><p>Read at least one byte of cooked data unless EOF is hit. Return <code class="docutils literal"><span class="pre">b''</span></code> if
EOF is hit.  Block if no data is immediately available.</p>
</dd></dl>

<dl class="method">
<dt id="telnetlib.Telnet.read_very_eager">
<code class="descclassname">Telnet.</code><code class="descname">read_very_eager</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#telnetlib.Telnet.read_very_eager" title="Permalink to this definition">¶</a></dt>
<dd><p>Read everything that can be without blocking in I/O (eager).</p>
<p>Raise <a class="reference internal" href="exceptions.html#EOFError" title="EOFError"><code class="xref py py-exc docutils literal"><span class="pre">EOFError</span></code></a> if connection closed and no cooked data available.
Return <code class="docutils literal"><span class="pre">b''</span></code> if no cooked data available otherwise. Do not block unless in
the midst of an IAC sequence.</p>
</dd></dl>

<dl class="method">
<dt id="telnetlib.Telnet.read_eager">
<code class="descclassname">Telnet.</code><code class="descname">read_eager</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#telnetlib.Telnet.read_eager" title="Permalink to this definition">¶</a></dt>
<dd><p>Read readily available data.</p>
<p>Raise <a class="reference internal" href="exceptions.html#EOFError" title="EOFError"><code class="xref py py-exc docutils literal"><span class="pre">EOFError</span></code></a> if connection closed and no cooked data available.
Return <code class="docutils literal"><span class="pre">b''</span></code> if no cooked data available otherwise. Do not block unless in
the midst of an IAC sequence.</p>
</dd></dl>

<dl class="method">
<dt id="telnetlib.Telnet.read_lazy">
<code class="descclassname">Telnet.</code><code class="descname">read_lazy</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#telnetlib.Telnet.read_lazy" title="Permalink to this definition">¶</a></dt>
<dd><p>Process and return data already in the queues (lazy).</p>
<p>Raise <a class="reference internal" href="exceptions.html#EOFError" title="EOFError"><code class="xref py py-exc docutils literal"><span class="pre">EOFError</span></code></a> if connection closed and no data available. Return
<code class="docutils literal"><span class="pre">b''</span></code> if no cooked data available otherwise.  Do not block unless in the
midst of an IAC sequence.</p>
</dd></dl>

<dl class="method">
<dt id="telnetlib.Telnet.read_very_lazy">
<code class="descclassname">Telnet.</code><code class="descname">read_very_lazy</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#telnetlib.Telnet.read_very_lazy" title="Permalink to this definition">¶</a></dt>
<dd><p>Return any data available in the cooked queue (very lazy).</p>
<p>Raise <a class="reference internal" href="exceptions.html#EOFError" title="EOFError"><code class="xref py py-exc docutils literal"><span class="pre">EOFError</span></code></a> if connection closed and no data available. Return
<code class="docutils literal"><span class="pre">b''</span></code> if no cooked data available otherwise.  This method never blocks.</p>
</dd></dl>

<dl class="method">
<dt id="telnetlib.Telnet.read_sb_data">
<code class="descclassname">Telnet.</code><code class="descname">read_sb_data</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#telnetlib.Telnet.read_sb_data" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the data collected between a SB/SE pair (suboption begin/end). The
callback should access these data when it was invoked with a <code class="docutils literal"><span class="pre">SE</span></code> command.
This method never blocks.</p>
</dd></dl>

<dl class="method">
<dt id="telnetlib.Telnet.open">
<code class="descclassname">Telnet.</code><code class="descname">open</code><span class="sig-paren">(</span><em>host</em>, <em>port=0</em><span class="optional">[</span>, <em>timeout</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#telnetlib.Telnet.open" title="Permalink to this definition">¶</a></dt>
<dd><p>Connect to a host. The optional second argument is the port number, which
defaults to the standard Telnet port (23). The optional <em>timeout</em> parameter
specifies a timeout in seconds for blocking operations like the connection
attempt (if not specified, the global default timeout setting will be used).</p>
<p>Do not try to reopen an already connected instance.</p>
</dd></dl>

<dl class="method">
<dt id="telnetlib.Telnet.msg">
<code class="descclassname">Telnet.</code><code class="descname">msg</code><span class="sig-paren">(</span><em>msg</em>, <em>*args</em><span class="sig-paren">)</span><a class="headerlink" href="#telnetlib.Telnet.msg" title="Permalink to this definition">¶</a></dt>
<dd><p>Print a debug message when the debug level is <code class="docutils literal"><span class="pre">&gt;</span></code> 0. If extra arguments are
present, they are substituted in the message using the standard string
formatting operator.</p>
</dd></dl>

<dl class="method">
<dt id="telnetlib.Telnet.set_debuglevel">
<code class="descclassname">Telnet.</code><code class="descname">set_debuglevel</code><span class="sig-paren">(</span><em>debuglevel</em><span class="sig-paren">)</span><a class="headerlink" href="#telnetlib.Telnet.set_debuglevel" title="Permalink to this definition">¶</a></dt>
<dd><p>Set the debug level.  The higher the value of <em>debuglevel</em>, the more debug
output you get (on <code class="docutils literal"><span class="pre">sys.stdout</span></code>).</p>
</dd></dl>

<dl class="method">
<dt id="telnetlib.Telnet.close">
<code class="descclassname">Telnet.</code><code class="descname">close</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#telnetlib.Telnet.close" title="Permalink to this definition">¶</a></dt>
<dd><p>Close the connection.</p>
</dd></dl>

<dl class="method">
<dt id="telnetlib.Telnet.get_socket">
<code class="descclassname">Telnet.</code><code class="descname">get_socket</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#telnetlib.Telnet.get_socket" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the socket object used internally.</p>
</dd></dl>

<dl class="method">
<dt id="telnetlib.Telnet.fileno">
<code class="descclassname">Telnet.</code><code class="descname">fileno</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#telnetlib.Telnet.fileno" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the file descriptor of the socket object used internally.</p>
</dd></dl>

<dl class="method">
<dt id="telnetlib.Telnet.write">
<code class="descclassname">Telnet.</code><code class="descname">write</code><span class="sig-paren">(</span><em>buffer</em><span class="sig-paren">)</span><a class="headerlink" href="#telnetlib.Telnet.write" title="Permalink to this definition">¶</a></dt>
<dd><p>Write a byte string to the socket, doubling any IAC characters. This can
block if the connection is blocked.  May raise <a class="reference internal" href="exceptions.html#OSError" title="OSError"><code class="xref py py-exc docutils literal"><span class="pre">OSError</span></code></a> if the
connection is closed.</p>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.3: </span>This method used to raise <a class="reference internal" href="socket.html#socket.error" title="socket.error"><code class="xref py py-exc docutils literal"><span class="pre">socket.error</span></code></a>, which is now an alias
of <a class="reference internal" href="exceptions.html#OSError" title="OSError"><code class="xref py py-exc docutils literal"><span class="pre">OSError</span></code></a>.</p>
</div>
</dd></dl>

<dl class="method">
<dt id="telnetlib.Telnet.interact">
<code class="descclassname">Telnet.</code><code class="descname">interact</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#telnetlib.Telnet.interact" title="Permalink to this definition">¶</a></dt>
<dd><p>Interaction function, emulates a very dumb Telnet client.</p>
</dd></dl>

<dl class="method">
<dt id="telnetlib.Telnet.mt_interact">
<code class="descclassname">Telnet.</code><code class="descname">mt_interact</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#telnetlib.Telnet.mt_interact" title="Permalink to this definition">¶</a></dt>
<dd><p>Multithreaded version of <a class="reference internal" href="#telnetlib.Telnet.interact" title="telnetlib.Telnet.interact"><code class="xref py py-meth docutils literal"><span class="pre">interact()</span></code></a>.</p>
</dd></dl>

<dl class="method">
<dt id="telnetlib.Telnet.expect">
<code class="descclassname">Telnet.</code><code class="descname">expect</code><span class="sig-paren">(</span><em>list</em>, <em>timeout=None</em><span class="sig-paren">)</span><a class="headerlink" href="#telnetlib.Telnet.expect" title="Permalink to this definition">¶</a></dt>
<dd><p>Read until one from a list of a regular expressions matches.</p>
<p>The first argument is a list of regular expressions, either compiled
(<a class="reference internal" href="re.html#re-objects"><span class="std std-ref">regex objects</span></a>) or uncompiled (byte strings). The
optional second argument is a timeout, in seconds; the default is to block
indefinitely.</p>
<p>Return a tuple of three items: the index in the list of the first regular
expression that matches; the match object returned; and the bytes read up
till and including the match.</p>
<p>If end of file is found and no bytes were read, raise <a class="reference internal" href="exceptions.html#EOFError" title="EOFError"><code class="xref py py-exc docutils literal"><span class="pre">EOFError</span></code></a>.
Otherwise, when nothing matches, return <code class="docutils literal"><span class="pre">(-1,</span> <span class="pre">None,</span> <span class="pre">data)</span></code> where <em>data</em> is
the bytes received so far (may be empty bytes if a timeout happened).</p>
<p>If a regular expression ends with a greedy match (such as <code class="docutils literal"><span class="pre">.*</span></code>) or if more
than one expression can match the same input, the results are
non-deterministic, and may depend on the I/O timing.</p>
</dd></dl>

<dl class="method">
<dt id="telnetlib.Telnet.set_option_negotiation_callback">
<code class="descclassname">Telnet.</code><code class="descname">set_option_negotiation_callback</code><span class="sig-paren">(</span><em>callback</em><span class="sig-paren">)</span><a class="headerlink" href="#telnetlib.Telnet.set_option_negotiation_callback" title="Permalink to this definition">¶</a></dt>
<dd><p>Each time a telnet option is read on the input flow, this <em>callback</em> (if set) is
called with the following parameters: callback(telnet socket, command
(DO/DONT/WILL/WONT), option).  No other action is done afterwards by telnetlib.</p>
</dd></dl>

</div>
<div class="section" id="telnet-example">
<span id="id2"></span><h2>21.19.2. Telnet Example<a class="headerlink" href="#telnet-example" title="Permalink to this headline">¶</a></h2>
<p>A simple example illustrating typical use:</p>
<div class="highlight-python3"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">getpass</span>
<span class="kn">import</span> <span class="nn">telnetlib</span>

<span class="n">HOST</span> <span class="o">=</span> <span class="s2">&quot;localhost&quot;</span>
<span class="n">user</span> <span class="o">=</span> <span class="nb">input</span><span class="p">(</span><span class="s2">&quot;Enter your remote account: &quot;</span><span class="p">)</span>
<span class="n">password</span> <span class="o">=</span> <span class="n">getpass</span><span class="o">.</span><span class="n">getpass</span><span class="p">()</span>

<span class="n">tn</span> <span class="o">=</span> <span class="n">telnetlib</span><span class="o">.</span><span class="n">Telnet</span><span class="p">(</span><span class="n">HOST</span><span class="p">)</span>

<span class="n">tn</span><span class="o">.</span><span class="n">read_until</span><span class="p">(</span><span class="sa">b</span><span class="s2">&quot;login: &quot;</span><span class="p">)</span>
<span class="n">tn</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="n">user</span><span class="o">.</span><span class="n">encode</span><span class="p">(</span><span class="s1">&#39;ascii&#39;</span><span class="p">)</span> <span class="o">+</span> <span class="sa">b</span><span class="s2">&quot;</span><span class="se">\n</span><span class="s2">&quot;</span><span class="p">)</span>
<span class="k">if</span> <span class="n">password</span><span class="p">:</span>
    <span class="n">tn</span><span class="o">.</span><span class="n">read_until</span><span class="p">(</span><span class="sa">b</span><span class="s2">&quot;Password: &quot;</span><span class="p">)</span>
    <span class="n">tn</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="n">password</span><span class="o">.</span><span class="n">encode</span><span class="p">(</span><span class="s1">&#39;ascii&#39;</span><span class="p">)</span> <span class="o">+</span> <span class="sa">b</span><span class="s2">&quot;</span><span class="se">\n</span><span class="s2">&quot;</span><span class="p">)</span>

<span class="n">tn</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="sa">b</span><span class="s2">&quot;ls</span><span class="se">\n</span><span class="s2">&quot;</span><span class="p">)</span>
<span class="n">tn</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="sa">b</span><span class="s2">&quot;exit</span><span class="se">\n</span><span class="s2">&quot;</span><span class="p">)</span>

<span class="nb">print</span><span class="p">(</span><span class="n">tn</span><span class="o">.</span><span class="n">read_all</span><span class="p">()</span><span class="o">.</span><span class="n">decode</span><span class="p">(</span><span class="s1">&#39;ascii&#39;</span><span class="p">))</span>
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